One great example of this is the McGurk Effect. Watch the video below and listen to the sound that the man is making. Make sure you are watching the man talk. Then close your eyes. Does the sound change based on whether you are watching him or not?
This effect is produced by visually recording the man making one sound and then dubbing a separate sound for the audio. The interesting thing is, that for many, you can look away and look back and the sound will change for you depending on whether you are looking at the man speaking or not.